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Two U.S. forces, not pictured here, were killed in Afghanistan Friday by an Afghan policeman. Just a day earlier, a Black Hawk helicopter crashed in southern Afghanistan killing 11 people, including seven American service members.

The U.S. military is now requiring all personnel in Afghanistan to keep a fully-loaded magazine in their weapons at all times, following a spate of attacks on American troops by members of Afghan forces.

A senior military official told NBC News of the new policy Friday, just after an Afghan policeman — whom NATO forces had just handed a new weapon as a present — opened fire, killing two U.S. Special Forces service members.

That shooting in western Afghanistan was just the latest in a recent string of insider, or "green-on-blue," attacks on coalition forces. Such attacks left six U.S. Marines dead in two separate incidents last Friday.

The new requirement "could save precious seconds," the official told NBC News, in responding to the attacks and could save lives — but the official acknowledged that any rogue armed Afghan officer or soldier "could always get the drop on" allied troops.

Alongside the new requirement, the U.S. Army is also requiring that one soldier, designated a "guardian angel," stand in a protected space with his weapon loaded at any gathering of U.S. military and armed Afghan security forces in order to enable a swift response to any threat.

The attacker in Friday's shooting had been recruited five days prior, and the Americans were in Farah province to hand out weapons and train new recruits, the province's deputy police chief told NBC News.

A NATO spokesman confirmed that the Afghan attacker was later shot and killed.

Col. Hagen Messer, spokesman for the International Joint Command in the country, confirmed the deaths in a statement. "Officials are investigating the incident to determine the facts and as more information becomes available it will be released as appropriate," he said.

The killing, the sixth similar incident in two weeks, occurred around 8 a.m. local time after U.S. forces arrived in Kinisk to train members of the local Afghan police force, Farah provincial police chief Agha Noor Kemtoz told The Associated Press.

Attacks by Afghan allies on international troops have accelerated this year. At least 36 foreign troops have been killed, raising concerns about the strategy by coalition forces to train Afghan forces to take over the country's security when most foreign troops pull out in 2014.

The latest attack came one day after a Black Hawk helicopter crashed in southern Afghanistan, killing 11 people, including seven American service members. The dead included two Navy SEALs and a Navy expert in explosive ordnance disposal, as well as three Afghan soldiers and an Afghan interpreter.

NATO said an investigation into the cause of the helicopter crash was still ongoing, but U.S. officials told NBC news that the chopper was shot down, a claim confirmed by a provincial government spokesman. The Taliban has claimed responsibility for bringing it down.

And last week seven American service members, including a senior U.S. officer, were killed in Afghanistan in three separate attacks.